The inventor has more than twenty years experience in professional photography and photographic lighting. This work has frequently involved both moving and stationary subject matter illuminated by electronic flash. In some of these situations, the available methods of synchronizing the electronic flash with leaf shutter type cameras limited the inventor's ability to produce a visualized result.
In the majority of cameras, and in all professional cameras equipped with leaf-type shutters, the closing of the flash contacts which discharges the electronic flash occurs at the instant of shutter opening. For most general photography this arrangement is satisfactory and it has the advantage of making the entire duration of shutter opening available for the flash exposure.
The disadvantage to shutters which synchronize upon opening occurs when subjects are illuminated by strong ambient light in addition to electronic flash. Under these conditions unnatural "ghost images" are recorded. In the case of subjects in motion, motion streaks seem to precede the subject rather than follow it. This phenomenon is produced because the brief burst of electronic flash at the start of the exposure "freezes" the subject, which then continues to move while illuminated by ambient light for the remainder of the exposure and is recorded as a blur.
Several 35 mm single lens reflex, focal plane type shutter cameras are available with switch-selectable synchronization modes, so that the user can choose to discharge the electronic flash at shutter opening, or at shutter closure. To the inventor's knowledge, no such flash synchronization control is incorporated in the leaf shutter type cameras favored by professional photographers.